Increasing the sensitivity and reducing assay run time is often important for detecting and identifying microorganisms in clinical and environmental samples. For example, in the case of sepsis diagnosis, even a moderate increase in sensitivity or a decrease in assay time can have life or death consequences for a patient. In cell affinity assays in which increased sensitivity is required, it is common to augment the concentration of cell numbers at the proximity of the capture ligands, and to attempt to increase the frequency at which the cells collide with the capture ligands. Sample concentration, in the case of cellular samples, is routinely performed by centrifugation or filtration followed by cell re-suspension in an appropriate liquid media. Unfortunately, the processes require several time consuming manual steps and are not easily amenable to automation in a cost effective manner.
While some solutions have proposed the use of electric fields for the concentration and capture of species, such methods typically still require complex sample preparation steps in order to obtain a precisely controlled ionic environment. For example, in prior art devices adapted to produce concentration using electrophoretic concentration, it is usually necessary to re-suspend the sample in a buffer with a low ionic strength and/or to include oxidation and reduction reagents to avoid or mitigate electrolytic effects. A failure to address these effects results in problems associated with the difficulty of establishing an electric field inside a raw or minimally treated aqueous sample due to screening effects of the dissolved ions, and the onset of electrochemical reactions, such as water electrolysis, at the electrode-electrolyte interfaces. Such limitations impair the utility of electrical sample concentration approaches due to the onerous and costly pre-processing steps.
What is therefore needed is an integrated device that allows for the rapid concentration of analyte and the subsequent detection of a sample, without requiring significant pre-treatment of the sample.